106 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



that much larger quantities will not do if spread over longer periods. 

 "When the atmosphere is heavy and moisture-laden the fumes will be 

 less able to disperse, and then it is that most harm is done. Injury 

 may be caused not only to trees and shrubs, but also to grass and 

 thereby to stock feeding on it. I have known cases in which, from the 

 smelting of copper ores, comparatively large quantities of copper and of 

 arsenic, together with sulphurous acid, were carried for a distance of 

 two to three miles and seriously affected the herbage and the health of 

 stock, besides killing all trees and hedges in the direct course of the 

 fumes. Similarly brickworks, where the clay used contains a good deal 

 of pyrites, may emit a quantity of sulphurous acid and do injury alike 

 to foliage, grass, and stock. 



Ammonia gas, again, is very fatal to plant-life, and, to come to 

 matters of more daily concern to the gardener, I have known of cases 

 where irretrievable harm has been caused to plants through the coating of 

 greenhouses internally with tar that has contained a considerable quantity 

 of carbolic acid and other volatile products. The heat has caused these 

 to be given off and the plants have rapidly suffered. When this is the 

 case the trouble is one most difficult to get rid of ; limewashing will 

 avail somewhat, but time is needed until all exhalations that will come 

 off have done so. In one case brought to my notice, the gutters inside 

 a melon-house had been coated with a mixture of tar and paraffin, paint 

 being subsequently put on. The plants died and at the same time it 

 was noticed that "fumes" (as they were described) were given off from 

 the tar. I have no doubt that the injury arose from the presence of 

 volatile matters in the tar used. 



The difficulty with the detection of the cause of injury in all these 

 cases is to find on the injured plant or tree clear evidence of the 

 presence of the suspected ingredient. It is only indeed in the case of 

 certain heavy metals like copper, arsenic, &c, that the materials them- 

 selves can be found ; in many others the harm has been done and no 

 trace of the harmful material is left. So, too, a plant may be killed by 

 the use of carbolic acid, bisulphide of carbon, or other volatile substance 

 which will do the injury but then volatilise and not be capable of detection. 



Moisture. 



Next to the atmosphere comes, as an important factor in plant-life, 

 moisture. 'While soil is of great importance, moisture is perhaps more 

 so, as there is no soil that is absolutely devoid of nutriment, while 

 without moisture nothing whatever can be done. In most cultivated 

 plants, garden and farm crops, 90 per cent, of the total substance is 

 water, and even timber contains 40 per cent. A small amount may be 

 taken in directly by the leaves, but by far the greater part is obtained from 

 the soil and is utilised there in combination with dissolved gases for the 

 purpose of rendering the constituents, both from soil and manure, soluble. 

 The water is absorbed by the plant through its roots, and is transpired 

 through the leaves and other parts of the plant, thus causing the sap to 

 rise and drawing up the dissolved plant-food for distribution through the 

 entire structure. Hence the presence of moisture is of the greatest 



